Ice mass change in Greenland and Antarctica between 1993 and 2013 from satellite gravity measurements

We construct long-term time series of Greenland and Antarctic ice sheet mass change from satellite gravity measurements. A statistical reconstruction approach is developed based on a Principal Component Analysis to combine high-resolution spatial modes from the Gravity Recovery and Climate Experiment (GRACE) mission with the gravity information from conventional satellite track-ing data. Uncertainties of this reconstruction are rigorously assessed; they include temporal limitations for short GRACE measurements, spatial limitations for the low-resolution conventional tracking data measurements, and limitations of the estimated statistical relationships between low and high degree potential coe�cients re ected in the PCA modes. Trends of mass variations in Greenland and Antarctica are assessed against a number of previous studies. The resulting time series for Greenland show a higher rate of mass loss than other methods before 2000, while the Antarctic ice sheet appears heavily in uenced by interannual variations

All-electronic frequency stabilization of a DFB laser diode

A laser diode’s junction voltage is a sensitive measure of its temperature and can be used in a thermal control feedback loop. To compensate for the temperature dependence of the laser’s internal resistance, we have measured the dynamic resistance, ∂V/∂I, by modulating the injection current and measuring the demodulated voltage. The junction voltage was thus controlled while operating at fixed DC injection current. Over an external temperature range of 15°C to 35°C, this stabilised the centre frequency (wavelength) of a 1651 nm DFB laser diode with a residual mean frequency shift of 60 MHz (0.5pm), less than the uncertainty on the centre frequency of 80 MHz (0.7 pm). Under the same conditions, conventional thermistor control gave a systematic wavelength shift of −8.4 GHz (−76 pm), and control of the uncompensated forward voltage gave a shift of 9.9 GHz (90 pm)

An iterative ICA-based reconstruction method to produce consistent time-variable total water storage fields using GRACE and swarm satellite data

Observing global terrestrial water storage changes (TWSCs) from (inter-)seasonal to (multi-)decade time-scales is very important to understand the Earth as a system under natural and anthropogenic climate change. The primary goal of the Gravity Recovery And Climate Experiment (GRACE) satellite mission (2002–2017) and its follow-on mission (GRACE-FO, 2018–onward) is to provide time-variable gravity fields, which can be converted to TWSCs with ∼300 km spatial resolution; however, the one year data gap between GRACE and GRACE-FO represents a critical discontinuity, which cannot be replaced by alternative data or model with the same quality. To fill this gap, we applied time-variable gravity fields (2013–onward) from the Swarm Earth explorer mission with low spatial resolution of ∼1500 km. A novel iterative reconstruction approach was formulated based on the independent component analysis (ICA) that combines the GRACE and Swarm fields. The reconstructed TWSC fields of 2003–2018 were compared with a commonly applied reconstruction technique and GRACE-FO TWSC fields, whose results indicate a considerable noise reduction and long-term consistency improvement of the iterative ICA reconstruction technique. They were applied to evaluate trends and seasonal mass changes (of 2003–2018) within the world’s 33 largest river basin

Characterization of the Morphometry of Impact Craters Hosting Polar Deposits in Mercury's North Polar Region

Earth-based radar images dating back two decades show that the floors of some polar craters on Mercury host radar-bright deposits that have been proposed to consist of frozen volatiles. Several hypotheses have been put forth to explain their source, including volcanic outgassing, chemical sputtering, and deposition of exogenous water ice. Calculations show that volatiles are thermally stable in permanently shadowed areas. An earlier study of the depths of north polar craters determined with photoclinometric techniques applied to Mariner 10 images yielded the conclusion that the mean ratio of crater depth d to rim-crest diameter D for craters hosting polar deposits is two-thirds that of the mean ratio for a comparable population of neighboring craters lacking such deposits. This result could be explained by (though doesn't require) the presence of a thick layer of volatiles within the polar deposit-hosting craters. Here we use altimetric profiles and topographic maps obtained by the Mercury Laser Altimeter (MLA) to revisit this analysis. MLA is an instrument on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, which has been orbiting Mercury since March 2011. MLA transmits a 1064-nm laser pulse at 8 Hz during MESSENGER's trajectory over Mercury s surface. The MLA illuminates surface areas averaging between 15 m and 100 m in diameter, spaced approx 400 m apart along the spacecraft ground track. The radial precision of individual measurements is <1 m, and the current accuracy with respect to Mercury s center of mass is better than 20 m. As of mid-December 2011, MLA coverage had reached to 15 S and has yielded a comprehensive map of the topography of Mercury s northern hemisphere. The MLA data are used here to quantify the shapes of craters in the north polar region and to avoid the shadowing bias of photoclinometric techniques

Extending the Record of Time-Variable Gravity by Combining Grace and Conventional Tracking Data

The Gravity Recovery and Climate Experiment (GRACE) mission has provided invaluable insight on the behavior of mass redistribution on the surface of the Earth since its launch in March 2002. GRACE measures the range between its two satellites to obtain a new, high-resolution, global gravity field of the Earth every month. This dissertation presents the first record of high-resolution time-variable gravity that extends to the 1990s. This gravity reconstruction is obtained by combining GRACE with gravity solutions generated from conventional tracking of satellites that start in November 1992. These tracking observations originate from two ground-based systems, Satellite Laser Ranging (SLR) and Doppler Orbitography and Radiopositioning Integrated by Satellites (DORIS). The statistical framework for the reconstructions of the two fields can be described in three major steps. First, high-resolution spatial patterns are obtained from a Principal Component Analysis (PCA) decomposition of GRACE gravity coefficients. In the second step, the top four patterns are used as the model relating the SLR/DORIS coefficients to their temporal modulation, which are solved for in a Least Squares Adjustment. Lastly, the full patterns and their temporal modulation are linearly combined to form gravity fields that span the SLR/DORIS time frame and therefore add a decade of perspective before GRACE. An error budget is also designed to quantify the influence of assumptions made in the reconstruction. The primary scientific goal was to add perspective on the behavior of polar ice sheet melt in the 1990s. The second goal was to extend the record of terrestrial water storage. One last application examined the possibility of using this technique as a way to bridge the upcoming multi-month gap between GRACE and its successor mission, GRACE Follow-On

Improved survival of orthotopic liver allograft in swine by addition of trophic factors to University of Wisconsin solution.

Serum-free preservation media such as University of Wisconsin (UW) may cause tissue damage through trophic factor (TF) deprivation. This study evaluated whether the addition of TFs to UW solution improves liver graft quality after extended cold preservation time in pigs. UW solution was supplemented with epidermal growth factor, insulin-like growth factor-1, nerve growth factor-beta, bactenecin, and substance P to create TF-supplemented (TFS) UW. Orthotopic liver transplantation was performed after 18 hr of static cold storage at 4 degrees C in UW (n=7) or TFS-UW (n=7) solution. Recipients of grafts preserved with TFS-UW demonstrated significantly better 5-day survival (57%) than those preserved with UW alone (14%) (P<0.05). Adenosine triphosphate content in grafts preserved in TFS-UW was significantly higher than in grafts preserved in UW (17.4+/-5.0 vs. 4.8+/-1.2 nmol/mg protein, respectively) (P<0.05). This study showed that the addition of TFs to UW solution allowed a significant extension of cold ischemic time in pigs